Just basing the review purely on whats available and not if children should be here or not.
It does seem smooth, I was quite surprised. It has a happy little beat for background music. However, while I commend your efforts to offer more entertaining ways to learn, I fear that children would quickly tire of this for the following reasons:
1) age group is 2-10, granted there are children who have a hard time learning but by the age of 10 if they can't recite their ABC's and recognize numbers to 100 there are much more drastic measures that are needed . That being said, maybe lower the target group to say 2-6 or 7
2) young children are attracted to color. Did you think about using different colors for the orbs and having it display the correct color for the orb the child needs to choose? This way said target group is also able to get color practice in.
3) -1 second for clicking on the wrong answer. While I understand that all great stories must have a conflict, and likewise all games, this seems a harsh penalty for very young children who might need the whole minute or more to locate one or two items. Perhaps an option to toggle the timer on and off, that way as they improve their skills they can continue to challenge themselves by adding the timer.
4) Changing the shape of the playing field might keep attention longer as well, square, circle, triangle, star, and then back to square
5) Also having a way to actually shoot the balloon, ie darts, or have the mouse icon be a hand with a needle in it.
6) This is more of a note than any suggestion, having played through it several times and hearing the letters. All of them sound good, with the exception of Z. It should be pronounced either zed or zee but it sounds more like zeah.
Lol well... I certainly didn't mean to carry on that long. I apologize if this isn't what you were looking for. If you were looking for a yes it works or a no it doesn't work, then yes it does work and quite well. Again I commend your efforts to enhance learning by adding a degree of fun into it.